At the present time, estrogen is the only therapy approved to prevent bone loss in the early phases of the menopause. We have previously shown tht daily injections of hPTH-(1-34) prevent bone loss from the proximal femur and increase bone loss from the proximal femur and increae bone density in the spine in young women rendered estrogen deficient by administration of a GnRH analog for a period of 1 year. However, the effects of PTH on cortical bone remain unclear. The purpose of the proposed study is to determine whether daily injections of hPTH-(1-34) can prevent both cortical and trabecular bone loss in early postmenopausal women. The study also will investigate whether vriations in PTH dosage affect the skeletal response to PTH. We will also attempt to identify markers that predict the long-term skeletal response to PTH. Finally, by making comparisons with elderly osteoporotic women receiving the same PTH regimen (in a separate protocol submitted by Dr. Neer), we will assess the effects of aging and prior bone loss on the response to PTH.